Calcium Sensitivity of Glutamate Release in a Calyx-Type Terminal

Abstract

Synaptic efficacy critically depends on the presynaptic intracellular calcium concentration ([Ca2+]i). We measured the calcium sensitivity of glutamate release in a rat auditory brainstem synapse by laser photolysis of caged calcium. A rise in [Ca2+]i to 1 micromolar readily evoked release. An increase to >30 micromolar depleted the releasable vesicle pool in <0.5 millisecond. A comparison with action potential-evoked release suggested that a brief increase of [Ca2+]i to approximately 10 micromolar would be sufficient to reproduce the physiological release pattern. Thus, the calcium sensitivity of release at this synapse is high, and the distinction between phasic and delayed release is less pronounced than previously thought.

Mechanisms of Exocytosis in Insulin‐Secreting B‐Cells and Glucagon‐Secreting A‐Cells

“…of Ca 2π -dependent exocytosis in B-cells are around 20 mM (Takahashi et al 1997;Barg et al 2001a), and in fact similar to that of some neuronal terminals (Bollmann et al 2000;Beutner et al 2001). This value is surprisingly high because the average cytosolic (global) Ca 2π in the B-cell does not exceed ∂2 mM during stimulation (Ämmälä et al 1993;Bokvist et al 1995;Dryselius et al 1999).…”

“…Despite many similarities of the exocytotic machinery in (neuro-) endocrine cells and that in neurotransmitter-releasing fast synapses, there are important differences: 1) synaptic vesicles are small (diameter Ͻ30 nm; von Gersdorff 1996) compared with peptide containing vesicles (hundreds of nm; Plattner et al 1997;Olofsson et al 2002); 2) synaptic exocytosis occurs without delay after the influx of Ca 2π and is at least one order-of magnitude faster than peptide secretion (Ämmälä et al 1993;Mennerick & Matthews 1996); 3) synaptic vesicles may stay largely intact during exocytosis and are refilled with new transmitter molecules immediately after endocytosis, whereas peptide-containing granules are assembled and filled with secretory peptides in the Golgi apparatus (Betz & Bewick 1992;Hutton 1994); 4) synaptic exocytosis generally requires higher concentrations of Ca 2π (Ämmälä et al 1993;Mennerick & Matthews 1996, Chow et al 1996Bollmann et al 2000); and 5) although most secretory cells contain more than one type of voltage-gated Ca 2π -channel, synaptic transmitter exocytosis depends on the faster N-or P-type (Hirning et al 1988;Uchitel et al 1992), whereas endocrine cells preferentially use the L-type (Lopez et al 1994;Barg et al 2001a). Taken together, the findings in neurones suggest that the site of Ca 2π -influx is within minimal distance of the Ca 2π -sensor at the synaptic vesicle and functionally associated within release sites.…”

Ca2+from One or Two Channels Controls Fusion of a Single Vesicle at the Frog Neuromuscular Junction

“…Several models have been suggested for the Ca 2ϩ -dependent steps of release (Shahrezaei and Delaney, 2005). Here we use a high-affinity fast kinetic model suggested by Ca 2ϩ -uncaging experiments performed on the calyx of Held (Bollmann et al, 2000;Bollmann and Sakmann, 2005). We show that our results are robust against changes in the parameters of the release model.…”

“…The cooperative action of three to five Ca 2ϩ ions acting on the Ca 2ϩ sensor(s) of the release machinery is believed to be required to trigger fusion of synaptic vesicles (Dodge and Rahamimoff, 1967;Augustine and Charlton, 1986;Stanley, 1986;Heidelberger et al, 1994;Bollmann et al, 2000;Schneggenburger and Neher, 2000). The requirement for simultaneous binding of multiple Ca 2ϩ ions constitutes a "biochemical cooperativity" (Dodge and Rahamimoff, 1967).…”

CaV2.1 voltage activated calcium channels and synaptic transmission in familial hemiplegic migraine pathogenesis

“…Neurotransmitter release is a power function of presynaptic Ca 2+ current, with a power number between 3 and 4 (Dodge and Rahamimoff 1967, Bollmann et al 2000, Schneggenburger and Neher 2000, Mintz et al 1995. So, even small changes in presynaptic Ca 2+ influx have a large effect on the number of vesicles released by an action potential Regehr 1999, Meinrenken et al 2002).…”